The present invention relates generally to electrolysis cells, and more particularly to a water electrolysis cell for efficient production of hydrogen and oxygen using ultramicroelectrodes.
In water electrolysis, a potential is applied between an anode and a cathode immersed in an electrolyte to generate hydrogen at the cathode. Rate of hydrogen generation is dependent on the applied current and is independent of voltage above the minimum potential for electrolysis to proceed. The limitation on the current is directly related to electrolyte conductivity and electrode surface area. Conventional electrolysis cells include substantially two-dimensional plate electrodes. Electrolyte-electrode interface area is maximized by roughening, perforating or corrugating the electrode surface in order to increase current density and lower cell voltage, but current density has been substantially limited to about 1000 A/m.sup.2. Porous electrodes having high pore surface area approximate three-dimensional operation and may provide current densities up to 10,000 A/m.sup.2, but pore size, length and density are not uniform. The pores are tortious and closed at the ends which causes gas generated inside the pores to be confined by capillary action until the gas pressure exceeds the capillary forces. A central core of gas established inside the pore with a thin layer of electrolyte adhering to the pore walls results in an ohmic drop through the electrolyte film, which opposes the beneficial effect of increasing electrode surface area.
The invention solves or substantially reduces in critical importance problems with existing electrolysis cells as just suggested by providing a monopolar electrolysis cell structure in which a membrane separates the catholyte and anolyte chambers and allows only ion exchange between the chambers in order to separate the generated hydrogen and oxygen, and uses ultramicroelectrode particles with diameters in the micron size range as electrodes in order to maximize electrode surface area. The invention can be operated as a fluidized bed reactor by using electrolyte flow or by recycling a portion of the generated hydrogen or oxygen to keep the particles in suspension. The invention may be statically-fed to avoid electrolyte pumping and circulating. Use of ultramicroelectrodes according to the invention provides a large surface area to the flow of electrolyte, small diffusion layer, low ohmic losses, high current densities, and rapid time response with high rate of mass transfer and the associated high operating efficiencies, as compared to conventional cells containing planar electrodes.
Background material related to electrolysis generally which may be helpful in understanding the invention may be found by reference to Pulsed DC And Anode Depolarization In Water Electrolysis For Hydrogen Generation, by A. H. Shaaban, ESL-TR-92-55, Air Force Civil Engineering Support Agency, Tyndall Air Force Base FL (August 1994), and the references cited therein, the entire teachings of which are incorporated by reference herein.
It is therefore a principal object of the invention to provide an improved electrolysis cell.
It is another object of the invention to provide an electrolysis cell having high current density and operating efficiency.
It is another object of the invention to provide an electrolysis cell containing porous electrodes comprising ultramicroelectrode particles.
It is a further object of the invention to provide an electrolysis cell providing high current density and high reaction rate for the generation of hydrogen.
It is another object of the invention to provide an electrolysis cell for producing hydrogen and oxygen at about 99.99% purity.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.